1. Field of the Invention
The present invention relates to a filter element, and more particularly, to a filter element applicable to an air cleaner mounted to an internal combustion engine, for example.
2. Related Art
There is known, in a conventional technology, a filter element provided with a filter member that is formed by pleating a non-woven fabric (unwoven cloth) or filter paper along a width direction thereof and a holder frame that holds or supports an outer edge portion of the filter member.
As a prior art patent document, there is provided, for example, Japanese Patent Laid-open Publication No. HEI 10-263348 (Patent Document 1). A filter element disclosed in this Patent Document 1 is a filter element that is provided with a filter member and a holder frame that holds the filter member, and a packing is formed, by an injection molding, integrally with a peripheral portion of the holder frame.
As mentioned above, the filter element of the Patent Document 1 is formed integrally with the packing through the injection molding process at the peripheral portion of the holder frame, so that packing fitting working is eliminated and the number of members to be used is also reduced, which contributes to improvement in assembling workability and manufacturing cost saving.
By the way, the holder frame of the conventional filter element of the kind mentioned above is formed of a synthetic resin (such as polypropylene or nylon) having thermoplastic property. Specifically, the holder frame is preferably formed of a thermoplastic elastomer because the packing is formed at the peripheral portion of the holder frame.
Moreover, the filter element disclosed in the Patent Document 1 has a rib for reinforcing the holder frame in series along the longitudinal direction thereof. Such rib attains a function, in addition to the function of reinforcing the holder frame, of keeping and holding distance between adjacent gathers of the pleated filter member to prevent reduction of filtering area due to contacting and sticking of the adjacent gathers of the pleated filter member.
With the filter element of the structure mentioned above, in a case where a laminated non-woven fabric formed of a plurality of non-woven fabric layers bonded together as the filter member is used, if the holder frame is formed of a soft material such as thermoplastic elastomer, an external force will be applied concentrically to an end portion of the filter member when the filter element is intentionally twisted or bent. In such case, the end portion will be deformed, resulting in displacement of the end portion which may leads to separation or peel-off of the bonded laminated non-woven fabric layers or also to separation between the non-woven fabric and the holder frame, thus providing undesirable matter.